Demand meter



Patented May 28, 1935 PATE NT YoF'Fl-cE;

DEMAND METER Benjamin H. Smith, Bloomfield, N. J., assignor' to Westinghouse "Electric & Manufacturing Company East Pittsburgh, Pa., a corporation of Pennsylvania Application September 13, 1934, serial to. 743,866; a so aims. 01. 171-273) My invention relates to demand meters'and' particularly to such meters which operate mechanically to produce a lagged demandindica tion--which is an integrated function of the measured variable with respect to time. It'has heretofore been proposed to effect'the mechanical integrating operation necessary insuch "a meter by means of a'difierential" gear having one element "driven at a speed proportional to the measured variable and a second element driven at a variable speed proportional to the deflection of the third or planetary elementoi the difier ential gear. It may be shown'l that, with'such an arrangement, the deflection of the planetary element after a prolonged steady demand of any value is proportional to the value, and in response to a sudden change of demand, the deflection of the planetary element approaches the adjusted value along an exponential curve. For" example, if the demand has been We for a long change from W0 to zero may be represented as Where I "W=the instantaneous reading of the demand meter (deflection oi the planetary) v Wo=initial demand e=the base of natural logarithms -u.=a constant t:time. I 7

Similarly for a sudden increase of demand, the position oi'the planetary elementapproaches its adjusted value along the corresponding rising function (1e The exponential functions 6- and (l ewill be recognized as the time characteristics of so-called single-energy transients, that is, transients in which the rate of storage or'rate of dissipation of a stored quantityis proportional to the stored quantity. These curves are "fol lowed exactly by the voltage of a' condenser being charged or discharged through a resisto'r,'the inductive discharge current in'a circuit containing inductance and resistance, and similar physical phenomena such as the change of weight of'radioactive materials. They are also closely approximated by the temperature changes of electrical "machinery and by many complicated transients. Such exponential functions are, per; haps', the perfect standard for demand measurements as they most closely represent the strains imposed upon diversified apparatus under prolonged load. a V r I The differential arrangements heretbfoi eproposed, however, have not'come into commercial usebecause of the-mechanical difl iculties of "providing asuitable mechanism. I have foundthat I for proper operation of aidemandmeter of the type indicated above, itis'necessary that the planetary element' be rotatable freely Without a substantial mechanical load and without any mechanism shall be-providedwhich shall impose a minimum mechanical burden on the differential V v ear. V H

Another object of 'my invention is to' provide a novel demand meter "of the exponential type which shall be of simple and'rugge'd-construction. Otherobjects of my invention willbecome evident irom the following detailed description taken in conjunction with the accompanying drawing, inwhich T Figure 1 is a view in perspective of the principal 7 operating parts of'a demand meter embodying my invention, with parts broken away. V

'Fig. 2 is a diagrammatic view showing the contour of a cam usedin the practice of my invention;and,

Fig. 3 is a time-demand chart illustrating the operation of my invention. 7 P

1 Referring to Fig. 1, in'detail, aprimarymeter element i which may be the movable element of any continuous-motion form of meter, such as a watthour meter, is connected by means of suitablegearing 2 and a sleeve 4a to one driving ele- Inent 3a of a differential "gear 3. The second driving element 3bof the" differential-gear 3 is mounted on a sleeve and connected by means I of suitable "gearing 5 toa'cylinder 6,-to be driven disc I. "The direction of inclination of the cylinder 6 from the horizontal is such that the ball I0 rolls by gravity into contact with a cam I I.

The cam I I is secured to shaft I2 which passes freely through the sleeves 4a and 4b to suitable mechanism I 3 for driving a pusher I I. The pusher I 4 cooperates in the usual manner with a maximum pointer I5 and a dial I6. A gear wheel 30 is rotatably secured in a slot iIIa "in lihe cam H, in such manneras to engage theelements' 3a and 3b of the differential gear 3. With this construction, the cam I I forms the planetary element of the differential gear 3.

The relative positions of the cylinder 6 and timjing disc 7 are such that when the point-of contact of the ball I!) with the cam :H at the angular position of the latter correspondingl'to zero reading of'the pointer I5, the ball I0 touches the disc I at its exact center. The iom'itorur of the Zoom II is such that upon angular movement of the cam from its zero position, the ball Ill 'is'moved pusher ld'is :at'n )PQS'ilt'iGl'l as shown; Under these (conditions, the elements 3a and 3b" are being. ntasubstantially equal speeds the same direction as indicatedhynr rows. If the idemand suddenly falls to zero, the mete element I and the part do of the differential ggear cease to rotate However, \the element 317 nontinues to driven, ,in the direction indicated by. the snow. by means of 'thenylinder 6 and lball ID from the synchronous motor 9. The rotation of element 31) drivesthe cam 2H :atha-lf the speed of element 131; toward the zeroposition of :pusher I4. However, :as the team M rotates "toward zero position, the ,point :of contact iof the hall \I 0 with the "timing disc 3 approaches the center of.

the latter, and the speed of cylinder *5 and Isle: ment 3b fall proportionately.

Thewcam H and pusher I4 .acoondingly zapproa'ch gtheir .zeno positions at a gradually ide-.

creasing rate. ,ASzfihG rate of change of deflection 0f the cam I I, i. \e., its speed, is proportional to its deflection, it maybe shown that its deflec tion follows the exponential law mentioned above.

, Referring-toliig. 8, in which the absoissae denote time and ordinates'denote demand, the exponentia-l curye of deflection of the pusher, :I4

following .a :dec-reasefof demand to zero is .ind-ik cated by the dotted curve section 411.. If the zero demand nondition persists for a isufficien-tly long time, the pusher deflection becomes zero.v Upon increase .of the demand to another .yalue such .as W2, the pusher deflection approaches the new value along a rising exponential curve section d2.

The Operation ,of .the meter correspondingf'to' the curve section d2 may be explained as follows:

- When the cam 'II finally reaches -its zero pos'ition, the ball Ill touches the timing disc "I at its latter. However, as the cam II rotates, the ball III is moved away from the center of timing disc I, and the element 3b commences to rotate in the direction of its arrow. The speed of cam I I gradually falls as the speed of' element 3b rises, until a conditionof equilibrium is reached at which the speed of element 31) exactly equals the speed of element 3a., and the cam II is stationary.

I do not intend that the present invention shall be restricted to the specific structural details, ar-

- rangement of parts or circuit connections herein set fomtln, as various modifications thereof may be effected without departing from the spirit and scope of my invention; I desire, therefore, that only :such limitations shall be imposed as are indicated in the appended claims.

7 I claim as my invention: e

f f 11.7111 a' demm'nd meter, a primary meter element operable at variable speed, a timing element operable at substantially constant speed, and variable-ratio transmission and differential mechanism connecting said elements, said mechanism including a pair of rotary members having adjacent non-engaging surfaces, at Toall in engagement'with said surfaces for transmitting the motion :of one to the other, at least one of said surfaces having a variable radius :along a path of movement of said ball, and differential means for moving said ball .along said path.

, 2. In :a demand meter, a primary meter .ele- I ment operable iatva-riable. speed, :a element operable :at substantially constant speed, and variable-ratio transmission and differential mechanism connecting said element-s, :said mechanism including *a ,pair of rotary members each having aisurface -of a geometrical .'-form traced Hey the revolution of a straight line, saidrotwrymemhers-being so positioned that a linear element or one surface is substantially gparallellto a linear element of the other surface, :at least one of :said

elements having-avariable radius along -the cor-- responding linear element, a rolling contact 1616- ment engagementwith said 'suzriaces, and means for moving said contact element in a direction parallel to said linear elements.

3. In a demandtineter, a primary :meter element operable atva-riiable speed, a timing :element operable at substantially constant-speed, and variable-ratio transmission and differential mechanism connecting said elements, :sa-id meohanism including a pair of rotary members each having :a surface :of a geometrical rform traced by the revolution of .a straight line, said rotary members #being -so positioned that :a linear element of one surface is substantially parallel to 4 a linear element of the other surface, 28,13 least one-=of said surfaces having a variable radius along the corresponding linear element, a ball in engagement with said surfaces and diifferential means for moving said ball in a directionparallel to said linear elements.

-4.',In a demand meter, :a primary meter element operable at variable speed a timing element operable at substantially constant speed, and variable-ratio transmission and differential mechanism connecting said elements, said mechanism including a cylinder and a disc mounted for rotation in such positions that .a linear element of the cylinder .is substantially parallel to a radius of the disc, a ball in engagement with the cylinder and the 'disc, and differential'means for moving the ball substantially parailel-to said linear-element of the cylinder.

.5. In a demand meter, a primary meter olement operable at variable speed, a timing eleential means for moving said ball along said ment operable at substantially constant speed, variable ratio transmission mechanism comprising a pair of rotary members having adjacent non-engaging surfaces, a ball in engagement with said surfaces for transmitting the motion of one of said surfaces to the other, at least one of said surfaces having a variable radius along a path of movement of said ball, differential mechanism comprising a pair of rotary members and diflerpath, means mechanically connecting one rotary member of said transmission mechanism to one rotary element of said differential mechanism, andmeans mechanically connecting said meter element and said timing element to the remaining rotary member of said transmission mechanism and said differential mechanism.

' BENJAMIN H. SMITH. 

